1. Field of the Invention
This invention relates to a pneumatic tire having a transponder therein for transmitting information concerning the tire, and to a method of and a device for reading and writing of a transponder.
2. Description of the Prior Art
The basic technique of a transponder which can transmit and receive at the same time has been established and has been adopted in various fields.
One application of the transponder is for pneumatic tires. The transponder is used in order to obtain information concerning the tire, inner pressure, temperature and the number of rotations, etc. For instance, a technique of receiving an information signal of the transponder after an electrical signal is transmitted to the transponder buried in the tire is shown in Japanese utility model application No. 2-123404.
The transponder comprises integrated circuits, coils and covers which protect this equipment. The shapes of the transponder can be coin shape, cylindrical shape, etc. and the transponder is relatively small. In the above application, edge portions of a carcass wound around bead cores and outer portions of the carcass in buttress portions (outer edge of a sidewall portion in a radial direction of the tire) are described for the portion in which the transponder is buried.
For adoption of the transponder to the tire, therefore, it is necessary to miniaturize the transponder and select locations to bury the transponder in view of durability carefully as well. For this reason, such limitations as described in the above mentioned application occur.
A device for reading and writing of the transponder (called reading device hereinafter) receiving and transmitting a signal to the transponder buried in a certain location is described in Japanese patent publication No. 4-501939 and U.S. Pat. No. 5,181,975.
Since the transponder is a foreign object to the tire, attention has to be paid to the durability when the transponder is buried in the tire. The internal environment of a tire is severe for electrical apparatus such as a transponder. Therefore, damage caused by an external force through the tire and heat generated in the tire should be prevented.
In the tire containing the transponder, the technique of communicating practically and stably with the transponder buried in the tire is a basic task. Further, an improvement of the durability which means protection of the transponder exposed in a severe environment such as the inside of the tire and deterioration of the tire caused by the transponder as well is necessary.
When reading and writing (called reading hereinafter) are done for the tire after dismounting from a vehicle, wherever the transponder is buried, reading can be done by searching all over the tire using devices described in the above mentioned applications or using a hand-held-reader, etc. If the location of the transponder is marked, the reading can be done much easier.
In the case of the reading for a tire mounted on a vehicle, the following should be considered:
1. The range which allows the reading of the transponder is restricted to about 30-50 cm; PA0 2. The transponder has a strong directivity; PA0 3. A clearance between the tire and the vehicle is restricted; PA0 4. In dual tires, since the tires are adjacent each other, interference is easily generated. PA0 1. For minimization of the transponder to be buried in the tire, a cylindrical shape is preferable. PA0 2. Installation of the transponder in the inner portion of the tire of the bead portion along an axial direction of the bead is preferable in order to prevent the above drawbacks as much as possible. This portion should not bring about disadvantages such as decreasing of range for reading and writing of the transponder caused by the interference of the transponder with steel cords. PA0 3. Since conventional transponders are used for animals, and from a requirement of water resistance property, it is covered by glass. Because the glass container is not durable enough to stand shocks when rim assembling and disassembling and when running, covers with excellent durability should preferably be adopted. Also, a heat resistance property and water resistance property over a long period necessary for the tire are required.
After many studies concerning the construction of the tire and the transponder which provide excellent durability, the present inventors have found the following: